1. Field of the Invention
The present invention relates to a double action push switch incorporated in cameras or electronic devices such as mobile phones. More particularly, it relates to a double action push switch used as the shutter release button of a mobile camera phone.
2. Description of the Related Art
FIG. 13 to FIG. 19B illustrate one known double action push switch.
A plate member 240 is accommodated in a cavity 201 formed in a housing 200. First, second, and third terminals 210, 220, 230 are fixed on the bottom plate of the housing 200, and their respective connecting portions 212, 222, 232 are protruded outside of the housing 200.
The open end of the cavity 201 is closed by a cover 250, which has a hole 251 at its center, through which an operating portion of a key top 260 protrudes to the outside. The cover 250 is fixed to the housing 200 by locking springs 252 formed on a side face of the cover 250, which engage with locking protrusions 203 protruded on an outer face of the housing 200.
As shown in FIGS. 19A and 19B, the plate member 240 consists of a domed center contact portion 241, an annular portion 244 around the center contact portion 241 separated therefrom by a pair of semi-circular arc holes 242 but continued therewith by a pair of coupling portions 243, and parallel rectangular plate-like peripheral contact portions 245 opposite each other on the outer periphery of the annular portion 244. The annular portion 244 is slanted downward from inside to outside and formed with wrinkles 246 at circumferentially equally spaced locations, each being offset by 90xc2x0.
The plate member 240 is initially in a resiliently deformed state inside the cavity 201 as it is held between an inner bottom face of the housing 200 and a lower face of the key top 260, as shown in FIG. 16 and FIG. 17. Its peripheral contact portions 245 are in contact with the contact points 211 of the first terminal 210.
When the key top 260 is pushed down, its pressing protrusion presses the center contact portion 241 of the plate member 240, inverting the annular portion 244. This first deformation causes the periphery of the center contact portion 241 to touch the contact points 221 of the second terminal 220, thereby establishing an electrical connection between the first and second terminals 210, 220.
When the key top 260 is pushed further down, its pressing protrusion presses the center contact portion 241 of the plate member 240 to cause further deformation. This second deformation causes the center of the center contact portion 241 to touch the contact point 231 of the third terminal 230, thereby establishing electrical connection between the first, second, and third terminals 210, 220, 230.
Since the prior art shown in FIG. 13 to FIG. 19B performs the two step connection with one plate member 240, the coupling portions 243 of the plate member 240 are subjected to too much stress, because of which the plate member 240 tends to break with fewer number of operation cycles.
Because the first deformation of the plate member 240 causes an inversion of the annular portion 244 which is formed by a bending process, and the second deformation causes inversion of the center contact portion 241 which is formed by a drawing process, stress is concentrated on the coupling portions 243, which connect the annular portion 244 and center contact portion 241. The coupling portions 243 are therefore particularly susceptible to cracks.
Another problem with the two step connection with one plate member 240 was that there was little freedom in setting different load characteristics for the first connection and the second connection.
That is, if the switch is designed to have desired load characteristics in the action of the first connection, then it inevitably has limitations in providing desired load characteristics for the action of the second connection.
The present inventors have designed a double action push switch as shown in Japanese Patent Application No. 2002-186830 that can resolve the above problems; FIG. 20 to FIG. 27C illustrate this push switch.
The housing 300 is formed with a cavity 301, and first, second, and third terminals 310, 320, 330 are fixed in the housing 300. Their respective contact points 311, 321, 331 are exposed in the inner bottom face of the cavity 301 on the outer side, inner side, and at the center, and their respective connecting portions 312, 322, 332 are protruded outside of the housing 300.
The open end of the cavity 301 is closed by a cover 340, which has a hole 341 at its center, through which an operating portion of a key top 350 protrudes to the outside. The cover 340 is fixed to the housing 300 by locking springs 342 formed on a side face of the cover 340 engaging with locking protrusion 303 protruded on an outer face of the housing 300.
The plate member accommodated inside the cavity 301 consists of first and second plates 360, 370 spaced apart in the up and down direction.
As shown in FIG. 25 to FIG. 27C, the first plate 360 is made up of a rectangular plate-like center contact portion 361, an annular portion 364 around the center contact portion 361 spaced away therefrom by a pair of semi-circular holes 362 and linked thereto by strips of coupling portions 363, and a pair of peripheral contact portions 365 on the outer periphery of the annular portion 364 at opposite locations. The center contact portion 361 has a downward protrusion 366 at its center and reinforcing upright portions 367 along the end edges of lengthwise direction. The annular portion 364 is formed with wrinkles 368 at circumferentially equally spaced locations.
The second plate 370 consists of two superposed pieces placed inside the cavity 301 as shown in FIGS. 22A and 22B, and has a dome-like shape protruding upwards.
When the key top 350 is pushed down, its pressing portion presses the center contact portion 361 of the first plate 360, inverting the coupling portions 363 as well as causing resilient deformation of the annular portion 364. This first deformation causes the protrusion 366 on the first plate 360 to touch the center of the second plate 370, whereby electrical connection is established between the first and second terminals 310, 320.
When the key top 350 is pushed further down, the protrusion 366 on the first plate 360 presses the center of the second plate 370 and causes it to invert. This second deformation causes the center of the second plate 370 to touch the contact point 331 of the third terminal 330, whereby electrical connection is achieved between the first, second, and third terminals 310, 320, 330.
Because the plate member consists of two plates 360, 370, both of them are not subjected to excessive stress. The plate member therefore has a longer life than the prior art with a single plate member. Also, this double action push switch can have a wider range of variations in its load characteristics because it has more freedom in designing the switch to attain desired load characteristics for each of the first and second switching actions.
The construction shown in FIG. 20 to FIG. 27C, however, has a problem that it occupies a relatively large mounting area on a printed circuit board because of large outer dimensions of the first plate 360.
More specifically, when the annular portion 364 of the first plate 360 has an outer diameter of 5.5 mm, and the second plate 370 has an outer diameter of 2.3 mm, the housing 300 has outer dimensions of 7.8 mmxc3x975.7 mm, measured in the top plan view of FIG. 20.
The prior art shown in FIG. 13 to FIG. 19B also has the problem of large mounting area on a printed circuit board because of large outer dimensions of the plate member 240 which performs the two step connecting action.
The present invention has been devised in view of the above problems, and an object of the invention is to provide a double action push switch having a longer life and more freedom in design to attain desired load characteristics for each step of switching actions and a smaller size so that it occupies less area on a printed circuit board.
A double action push switch according to an aspect of the present invention includes: a housing (1) formed with a cavity (13) therein; a first terminal (3), a second terminal (4), and a third terminal (5) fixed in the housing (1), respectively having contact points (31, 41, 51) exposed in an inner bottom face of the cavity (13); a first plate member (6) and a second plate member (7) placed side by side inside the cavity (13), both having a domed shape with their centers bulging away from the inner bottom face of the cavity (13), the first plate member (6) having its center and peripheral portion respectively abutting the contact points (31, 51) of the first and third terminals (3, 5), and the second plate member (7) having its center and peripheral portion abutting the contact points (41, 51) of the second and third terminals (4, 5); and a key top (8) having an operating portion (82) which is pressed for a double action switching operation and a first pressing portion (83) and a second pressing portion (84) for respectively pressing the centers of the first and second plate members (6, 7) for causing inversion thereof, the operating portion (82) being positioned at such a location that an operating load (P3) on the operating portion when a pressing point (K1) of the first pressing portion (83) on the first plate member (6) is a fulcrum and moments on the key top (8) are balanced is not equal to an operating load (P4) on the operating portion when a pressing point (K2) of the second pressing portion (84) on the second plate member (7) is a fulcrum and moments on the key top (8) are balanced. In this double action push switch configured above, a first pressing force applied to the operating portion (82) causes inversion of the center of one of the first plate member (6) and the second plate member (7) for achieving first electrical connection, and a second pressing force applied to the operating portion (82) causes inversion of the center of the other one of the first plate member (6) and the second plate member (7) for achieving second electrical connection.
With this configuration, when a pressing force is applied to the operating portion (82) of the key top (8), the first and second pressing portions (83, 84) of the key top (8) press the centers of the first and second plate members (6, 7) one after another and cause inversion of their centers.
Because the location of the operating portion (82) on the key top (8) is determined so that the operating load when one pressing point is the fulcrum is not equal to the operating load when the other pressing point is the fulcrum (P3 is not equal to P4), the pressing force first applied to the operating portion (82) causes inversion of the center of one of the first and second plate members (6, 7) so that it makes contact with two of the contact points (31, 41, 51) for achieving first electrical connection. The pressing force applied next to the operating portion (82) causes inversion of the center of the other one of the first and second plate members (6, 7) so that it makes contact with all of the contact points (31, 41, 51) for achieving second electrical connection.
According to another aspect of the invention, the first plate member (6) and the second plate member (7) can be constructed simply by forming them with identical load characteristics, and by setting the point on which the operating loads (P3, P4) are applied at a location offset from a mid point between the pressing points (K1, K2) of the first and second pressing portions on the first and second plate members (6, 7).
Alternatively, according to another aspect of the invention, the first plate member (6) and the second plate member (7) may have different load characteristics, and the point on which the operating loads (P3, P4) are applied may be made to coincide with a mid point between the pressing points (K1, K2) of the first and second pressing portions on the first and second plate members (6, 7). Thereby, the position at which the operating portion (82) is formed can readily be determined.
Alternatively, according to another aspect of the invention, the first plate member (6) and the second plate member (7) may have different load characteristics, and the point on which the operating loads (P3, P4) are applied may be offset from a mid point between the pressing points (K1, K2) of the first and second pressing portions on the first and second plate members (6, 7). Thereby, there will be more freedom in setting respective load characteristics such as clicking feeling for the first and second switching actions.
According to another aspect of the invention, the first, second, and third terminals (3, 4, 5) include respective connecting portions (33, 43, 53) protruding side by side from the housing (1) in a direction substantially the same as a direction in which the operating portion (82) of the key top (8) is pressed, so that the housing (1) is laterally mounted onto the printed circuit board (10), and that the operating portion (82) of the key top (8) is pressed in a direction parallel to the substrate face.
According to another aspect of the invention, the housing (1) includes stoppers (25) which will abut a substrate face at an edge portion of a recess (10a) formed in a printed circuit board (10) to which the housing (1) is mounted, so that the housing (1) does not protrude largely from the edge of the printed circuit board (10), and that the mounting of the housing (1) in the recess (10a) in the printed circuit board (10) is carried out easily.
A double action push switch according to another aspect of the invention includes: a first push switch (130) and a second push switch (140) mounted side by side on a printed circuit board (110), the first and second push switches (130, 140) respectively including a first key top (132) and a second key top (142), and a first plate member (133) and a second plate member (143) of a domed shape with their centers bulging towards the first and second key tops (132, 142); and an outer key top (150) disposed opposite the first and second key tops (132, 142), including an operating portion (152) protruded on one side and a first pressing portion (153) and a second pressing portion (154) protruded on the other side thereof, wherein
a pressing force applied to the operating portion (152) of the outer key top (150) causes the first and second pressing portions (153, 154) of the outer key top (150) to press the first and second key tops (132, 142), thereby causing inversion of one of the first plate member (133) and the second plate member (143) for achieving first electrical connection, and inversion of the other one of the first plate member (133) and the second plate member (143) for achieving second electrical connection, and
the operating portion of the outer key top (150) is positioned at such a location that an operating load (P3) on the operating portion (152) when a pressing point (K1) of the first pressing portion (153) on the first key top (132) is a fulcrum and moments on the outer key top (150) are balanced is not equal to an operating load (P4) on the operating portion (152) when a pressing point (K2) of the second pressing portion (154) on the second key top (142) is a fulcrum and moments on the outer key top (150) are balanced.
With this configuration, when a pressing force is applied to the operating portion (152) of the outer key top (150), the first and second pressing portions (153, 154) of the outer key top (150) press the first and second key tops (132, 142) of the first and second push switches (130, 140), thereby inverting the centers of the first and second plate members (133, 143) of the first and second push switches (130, 140) one after another.
Because the location of the operating portion (152) on the key top (150) is determined so that the operating load when one pressing portion is the fulcrum is not equal to the operating load when the other pressing point is the fulcrum (P3 is not equal to P4), the pressing force first applied to the operating portion (152) causes inversion of the center of one of the first and second plate members (133, 143) for achieving first electrical connection. The pressing force applied next to the operating portion (152) causes inversion of the center of the other one of the first and second plate members (133, 143) for achieving second electrical connection.
According to another aspect of the invention, the first plate member (133) and the second plate member (143) can be constructed simply by forming them with identical load characteristics, and by setting the point on which the operating loads (P3, P4) are applied at a location offset from a mid point between the pressing points (K1, K2) of the first and second pressing portions on the first and second key tops.
Alternatively, according to another aspect of the invention, the first plate member (133) and the second plate member (143) may have different load characteristics, and the point on which the operating loads (P3, P4) are applied may be made to coincide with a mid point between the pressing points (K3, K4) of the first and second pressing portions on the first and second key tops. Thereby, the position at which the operating portion (152) is formed can readily be determined.
Alternatively, according to another aspect of the invention, the first plate member (133) and the second plate member (143) may have different load characteristics, and the point on which the operating loads (P3, P4) are applied may be offset from a mid point between the pressing points (K1, K2) of the first and second pressing portions on the first and second key tops. Thereby, there will be more freedom in setting respective load characteristics such as clicking feeling for the first and second switching actions.
According to another aspect of the invention, the first and second push switches (130, 140) are mounted on the printed circuit board (10) side by side such that the first and second key tops (132, 142) are pressed in a direction parallel to a substrate face of the printed circuit board (10). Thus, the first and second push switches (130, 140) are mounted onto the printed circuit board (10) such that the operating portion (152) of the outer key top (150) is pressed in a direction parallel to the substrate face.